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SOFIA explores Europe’s night sky

At last, the airborne observatory SOFIA has returned to Germany! In the early hours of the morning on 16 September, the research aircraft landed safely at Stuttgart airport and was visited by about 2000 astronomy and aircraft enthusiasts over the following two days. On the third day, it took to the skies for its first scientific flight over Europe.##markend##

It is in the DNA of the SOFIA team to attempt the impossible and push the boundaries of scientific exploration. During this research flight over Europe, we conquered new horizons while respecting the territorial borders that crisscross the continent.

Image: DLR

Georg Mitscher, the first DLR pilot to visit the SOFIA flight deck during a mission.

These intricate, international borders are the main reason why SOFIA had not attempted a scientific flight within Europe until now. While the Schengen Agreement guarantees almost unlimited freedom for travellers on the ground, the situation in the air is more complicated. This is especially the case when you are registered as a state aircraft of the USA, have a NASA airworthiness certification, and cannot fly on standard air routes – all of which have caused confusion for some national Air Traffic Control (ATC) authorities in Europe.

In addition to coordinating all national, regional, oceanic and military ATC organisations, we had to obtain diplomatic clearance from every country on our planned flightpath, or within 20 nautical miles to either side of it. We also had to consider possible deviations from our original flight plan caused by unpredictable winds.

Image: DLR (CC-BY 3.0)

The flight plan FANNIE. Every SOFIA flight is not only numbered, but also given a name. The flight number is incremented chronologically for each departure. However, the flight name refers to the flight plan.

During the early planning stages, European airspace regulations felt like one of the primary objects we wanted to observe on the flight – a black hole. But the European ATC organisations offered excellent support, shining a light on the logistical darkness with their information.

However, despite our best preparations, plans for SOFIA’s first scientific flight over Europe came close to collapse. Unusually strong southerly winds meant we had to move our planned flight route 80 nautical miles to the north just two days before take-off. This new route led us through Irish airspace, for which we had no diplomatic overflight permit. To avoid this, the flight planners had to make additional changes to the flight plan – resulting in less time for scientific observations.

Then, on the morning of the flight, just as everything appeared to be coming together, we received a message warning us about the activation of a military ‘Danger Area’ on our planned route. Could the flight be rescheduled at short notice, with further reductions to the time available for scientific observations? Or, had our fears come true? Was it really impossible to plan a successful scientific flight for SOFIA in Europe?

Image: Marco Veit

A special sight at Stuttgart Airport: SOFIA opens the telescope door and shows the telescope mirror below.

The crew briefing was due to take place at 17:00. If we could not find a solution by then, the flight would have to be cancelled. But, to our relief, at 15:00, a solution appeared. For SOFIA, the ‘Danger Area’ was reduced to altitudes below 36,000 feet. We could not go around the problem, but we could easily fly over it at 41,000 feet.

Pride and happines were in the air. We were very delighted about the capabilities and cooperation of all involved European ATC and military authorities. But another setback was yet to come. Immediately after take-off, the radio in the flight deck buzzed with chatter from the air traffic controllers responsible for the upper airspace in southern Germany. Our flight plan, which we had coordinated weeks beforehand, and which had been approved that same day, was completely unknown to them. Was all our preparation in vain? Would we have the same problem each time we handed over to the next air traffic control cell?

Fortunately, that was not the case. From France onwards, the ATC coordination ran like clockwork – at times, better than in the USA, where continuous night landings at airports mean the night sky can be much more crowded. The peace and quiet in the cockpit even allowed guests on board SOFIA to visit the pilots, who were more than happy to answer their questions.

Image: NASA/SOFIA/Lynette Cook

SOFIA targets the surroundings of black holes: This artistic representation shows the galaxy Cygnus A, which was examined with the high-resolution infrared camera HAWC+ on board SOFIA during a flight over Southern California.

Smooth interactions between all the aviation partners involved made it possible to get to the right place at the right time to observe the black hole Mrk 231 during the night of Wednesday 18 September. Our scientists will now analyse the great data we collected, together with those collected from the black hole at the centre of another galaxy, Cygnus A, earlier this year.

At the end of the long, tense day came a long, successful night of astronomy. Our guests were happy to have been a part of a unique SOFIA flight and our scientists were happy with the great quality of the observations made from the skies above Europe. Our pilots were happy too, having worked with the various European ATC organisations and landed safely back in Stuttgart.

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Clemens Plank studied mechanical engineering with a focus on aerospace engineering and nuclear technology at the Technical Univeristy of Munich (TU Munich). He completed his dissertation at the Massachusetts Institute of Technology (MIT) in the United States, in which he investigated computer simulation of hydrogen deflagration.
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